Lambart, Charles (1600–60), 1st earl of Cavan , landowner, military commander and politician, was born in Ireland about May 1600, the eldest son of Sir Oliver Lambart (qv), 1st Baron Lambart of Cavan, and his wife, Hester, daughter of Sir William Fleetwood of Carrington Manor, Bedfordshire. On his father's death in 1618, Charles inherited sizeable estates in Westmeath, Roscommon, Cavan and King's County, along with equally sizeable debts, as well as succeeding his father to the barony. On reaching his majority, he was forced to borrow further and before long his lands were heavily mortgaged. An apparently promising solution to his financial woes was his marriage, before June 1625, to Jane, daughter of the wealthy Richard, Lord Robartes. However, Robartes subsequently reneged on his promises of a generous marriage portion and changed his will effectively to disinherit Jane. Despite innumerable representations to court and eventual legal action, Lambart did not receive a penny from either Robartes or his successor.
From the mid 1620s Lambart resided in Cornwall, the seat of the Robartes family, presumably in anticipation of eventually gaining some of his father-in-law's lands. He sat as MP for Bossiney in Cornwall in the 1626 and 1628–9 English parliaments, and in 1627 appears to have exercised a military command in the area. On 6 March 1627 he became seneschal for the county of Cavan and the town of Kells. He spent late 1627 and early 1628 in Ireland where, after some determined lobbying, he was granted a company of foot on 17 May 1628. While helpful, such favours did little to alleviate his deteriorating financial position, as a number of creditors pursued him through the Irish courts. This is probably the main reason for his long absences in England, where he had some property at Southampton.
The Irish government, headed by Sir Thomas Wentworth (qv) from 1633, regarded Lambart's absenteeism unfavourably, given that he held a military command in Ireland, and made a number of rulings in favour of his creditors. In April 1639 the Irish privy council found against Lambart's claims to lands at Bealick, Co. Mayo, and declared his patent void. By 1640 Lambart was nursing considerable personal grievances against leading figures in the Irish administration. After failing to secure a seat in the 1640 English parliament, he took his seat in the Irish house of lords which, in any case, proved an ideal platform for his opposition to the government.
From the outset of the second session of the 1640–41 parliament, which began in June, Lambart and many other protestant lords aligned themselves with the catholic opposition to the government. He may also have been acting in concert with opposition elements in the English parliament. The sustained criticism of Wentworth in both the English and the Irish parliaments led to his fall and eventual execution in the spring of 1641. However, Lambart also wanted Wentworth's chief ministers to be held accountable, particularly Sir Gerard Lowther (qv) and Sir Richard Bolton (qv), who had voided his patent to Bealick. On 27 February and 1 March 1641 Lambart led the campaign in the house of lords for the impeachment of Wentworth's ministers. In these debates he strongly upheld the right of the Irish parliament to impeach government ministers and clashed with James Butler (qv), earl of Ormond, who was the leader of the royalists in the Irish house of lords. Recognising Lambart's political clout, the king appointed him a member of the Irish privy council on 9 August 1641.
Lambart owed much of his new prominence to catholic support, but the eruption of a massive catholic rebellion in October 1641 changed everything. He was forced to flee his residence at Kilbeggan for Dublin, which was to act as a protestant enclave for the next decade, and he later estimated that the rebellion cost him £2,000 a year in lost rents. In November he was commissioned to raise his own regiment to fight the rebels, and on 12 May 1642 he was appointed governor of Dublin. Although the parliamentary lord lieutenant of Ireland, Lord Lisle (qv), later appointed someone else to this position, Lambart was eventually allowed to remain governor. From the start of 1642 he campaigned regularly against the rebels, usually under the generalship of Ormond. Despite their past differences, the two men worked well together, driving rebel forces out of the Dublin region by summer 1643. Although Lambart earned a reputation as a good commander, he acted in a heavy-handed manner in his dealings with civilians in Dublin and was involved in constant disputes with some of his colleagues in the Irish government, who complained against the illegality and arbitrariness of his military tribunals.
Rather surprisingly, given his previous incarnation as parliamentarian firebrand, he became a royalist after the outbreak of the English civil war in 1642, possibly due to his regard for Ormond, and supported Ormond's ultimately unsuccessful efforts to negotiate a military alliance between the king and the catholic confederation of Ireland during 1643–6. The king rewarded his loyalty by creating him earl of Cavan in April 1647. By then, the royalists had been defeated in England and Dublin passed into the hands of the English parliament later that year. He served under the parliamentarian authorities for a time, participating in campaigns against the catholic confederates and received a payment of £640 from the English parliament in March 1648. However, at some point in 1648–9, he was sidelined by the authorities who regarded him as suspect because of his royalist past. Following the final defeat of the rebels in 1653, Cavan was at last able to recover his lands, but twelve years of war had taken its toll, and he remained in serious financial difficulties. The republican government treated his pleas for relief with sympathy, granting him a pension and a lease of the manors of Clontarf and Arlaine, but broadly kept him at arms length.
Cavan probably spent the 1650s living at Finglas, Co. Dublin, where he appears on the 1659 census. In 1660 he was high sheriff of Co. Cavan. He lived just long enough to witness the restoration of the monarchy, from which he presumably would have benefited, had he not died on 25 June 1660. He was buried in St Patrick's cathedral, Dublin, on 4 July. After the death of his first wife in 1655, Lambart married Rose, daughter of Sir James Ware (qv) of Dublin, an antiquary and leading royalist. With his first wife, he had five sons and four daughters. He was succeeded by his eldest son, Richard.